This invention relates to a silver halide photographic light-sensitive material and more particularly to a silver halide photographic light-sensitive material which is high in sensitivity, excellent in photographic characteristics and, inter alia, less in sensitivity variation and stable in quality.
In recent years, there have been demands for highly sensitive silver halide photographic light-sensitive materials (hereinafter called a light-sensitive material) year by year from the various viewpoints, and many sensitizing techniques have been studied in all its aspects.
Among the studies on the sensitizing techniques relating to silver halide grains, there is, for example, the study in which the quantum efficiency of silver halide grains is theoretically computed to discuss the influence of grain-size distributions, which was published in the pre-print circulated in the Tokyo Symposium 1980 on the progress in photography, `Interactions between light and materials for photographic applications` p. 91. According to this study, it is suggested that the preparation of monodispersive emulsions may be effectual to improve a silver halide quantum efficiency, that is to say, it may be able to make a silver halide emulsion highly sensitive. On the other hand, as the other studies of sensitizing techniques, there are investigations of the most suitable chemical sensitization applicable to the silver halide emulsions. There are well-known sensitizers useful in chemical sensitization, such as a sulfur sensitizer, a selenium sensitizer, a reduction sensitizer, a nobel metal sensitizer and the like. The above-mentioned chemical sensitizers are used independently or in combination. In addition, there have been studied on various methods of further increasing the sensitization effects by making use of the above-mentioned chemical sensitizers. The studies thereon include, for example, a proposal of the method of chemically sensitizing silver halide grains in the presence of a silver halide solvent as disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter called Japanese Patent O.P.I. Publication) No. 30747/1983; a proposal of the metal of chemically sensitizing silver halide grains in the presence of a nitrogen-containing heterocyclic compound capable of forming a complex with silver as disclosed in Japanese Patent O.P.I. Publication No. 126526/1983; and the like.
It is also a publicly known technique that a spectral sensitizer is added to a silver halide emulsion to widen the inherent light-sensitive wavelength range of the silver halide emulsion and, thereby the emulsion is spectrally sensitized.
It is greatly contributable to the high sensitization of a light-sensitive material when choosing a spectral sensitizer having a high spectral sensitization efficiency to be used therein, that is also well-known.
As for the spectral sensitizers to be placed at the service for the above-mentioned purpose, they are chosen from those having such desirable characteristics as that the spectral sensitization wavelength range thereof is well fitted, and there occurs neither of any diffusion thereof to other light-sensitive layers and any interaction thereof with additives other than the spectral sensitizers.
The further desired requirements are the satisfactory reduction of sensitivity lowering, fog occurrence, dye stain occured after a sensitizing treatment or the like, when preserving a light-sensitive material containing spectral sensitizers. In particular, in the case if using spectral sensitizers in a multi-layered color photographic light-sensitive material, it is required to be high in sensitivity, excellent in color reproducibility, and stable in photographic characteristics, even if the material is preserved for a long period of time, as the essential requirements.
On the other hand, among the characteristics required for light-sensitive materials, the stability of quality is one of the important. It is essential that the various characteristics of light-sensitive materials are to constantly be stable. If they should be varied, the quality of a finally obtained image will inevitably be varied. If the variation is tried to compensated every time when it occurs, the light-sensitive material will seriously be complicated to handle. Among the variations of the characteristics, the variations of sensitivity will affect the light-sensitive material seriously, therefore, the scattering of sensitivity is required to inhibit at a minimum so that no practical trouble is caused. There may be some instances where such scattering of sensitivity of light-sensitive materials may be caused according to the preserved conditions during the period until the manufactured light-sensitive materials are used. It may, however, be prevented a light-sensitive material from scattering of the sensitivity thereof caused with the passage of time if the preserving conditions could be controlled. In contrast with the above, if a scattering occurs in manufacture, the problems thereof will be fatal. One of the causes thereof is a problem of the stability of the coating solution of a silver halide photographic emulsion (hereinafter called simply a coating solution). If there is a difference in the sensitivity of a silver halide between the cases of coating the same coating solution on a support immediately after the solution is prepared and after standing of the solution, i.e., if the coating solution stability is poor, it is hard to mass-produce the light-sensitive materials constant in quality.
Such coating solution stability will depend upon the kinds of spectral sensitizers to be used for spectrally sensitizing a silver halide emulsion. Therefore, even if a spectral sensitizer is high in spectral sensitization efficiency, useful for a high sensitization and capable of displaying various characteristics required for the above-mentioned spectral sensitizers, such a spectral sensitizer is very hard to put in practical use if the coating solution stability thereof is poor.
The methods of improving the coating solution stability include, for example, a method of adding an azole, an azaindene compound or the like which have been known as stabilizers, such as a method of adding such a reducing agent as a hydroquinone or a sulfin; or a method of using some specific copolymer and an optical brightening agent in combination as described in Japanese Patent O.P.I. Publication No. 111629/1974. It may not be said that these methods are able to satisfactorily improve a coating solution stability and, in addition, some of the methods have such a disadvantage as that important photographic characteristics such as gradation and sensitivity are deteriorated.
Besides the above-mentioned methods, there is a method of adding a spectral sensitizer into a coating solution. However, this method had a disadvantage that residual color-stains caused by the spectral sensitizers are of frequent occurrence.